issued  April  1,1911. 

DEPARTMENT  OF?  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN  153. 

A.  D.  MELVIN,  CHIEF  OF  BUREAU. 


DE  :RMINATION  OF  NICOTIN 


IN  NICOTIN  SOL    IONS  AND 


TOBACCO  EXTRACTS 


California 


BY 


ROBERT  M.  CHAPIN, 

Senior  Biochemist^  Biochemic  Division, 


BARLCWCMED; 

742  NCR" 

NGELES,  , 


WASHINGTON: 
GOVERNMENT    PRINTING    OFFICE. 

1911. 


r 


Issued  April  1, 1911. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN  133. 

A.  D.  MELVIN,  CHIEF  OF  BUREAU. 


THE  DETERMINATION  OF  NICOTIN 

IN  NICOTIN  SOLUTIONS  AND 

TOBACCO  EXTRACTS 


BY 

ROBERT  M.  CHAPIN, 

Senior  Biochemist,- Biochemic  Division. 


LIBRARY  OF  THE 
LA.  CO.  MEDICAL ASSIt 

634  SOUTH  WESTLAKE 
LOS  ANGELES 


WASHINGTON: 
GOVERNMENT    PRINTING    OFFir  tj. 

1911 


THE  BUREAU  OF  ANIMAL  INDUSTRY. 


Chief:  A.  D.  MELVIN. 
Assistant  Chief:  A.  M.  FARRINGTON. 
Chief  Cleric:  CHARLES  C.  CARROLL. 
Animal  Husbandry  Division:  GEORGE  M.  ROMMEL,  chief. 
Biochemic  Division:  M.  DORSET,  chief. 
Dairy  Division:  B.  H.  RAWL,  chief. 

Inspection  Division:  RICE  P.  STEDDOM,  chief;  MORRIS  WOODEN,  R.  A.  RAMSAY, 
and  ALBERT  E.  BEHNKE,  associate  chiefs. 
Pathological  Division:  JOHN  R.  MOHLER,  chief. 
Quarantine  Division:  RICHARD  W.  HICKMAN,  chief. 
Zoological  Division:  B.  H.  RANSOM,  chief. 
Experiment  Division:  E.  C.  SCHROEDER,  superintendent. 
Editor:  JAMES  M.  PICKENS. 

2 


LETTER  OF  TRANSM1TTAL. 


U.  S.  DEPARTMENT  or  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY, 
Washington,  D.  C.,  January  11,  1911. 

SIR  :  I  have  the  honor  to  transmit  herewith  a  paper  on  "  The  De- 
termination of  Nicotin  in  Nicotin  Solutions  and  Tobacco  Extracts  " 
by  Mr.  Kobert  M.  Chapin,  Senior  Biochemist  in  the  Biochemic  Divi- 
sion of  this  bureau,  and  to  recommend  its  publication  in  the  bulletin 
series  of  the  bureau. 

This  paper  describes  an  accurate  and  rapid  method  for  the  deter- 
mination of  nicotin,  the  method  being  applicable  especially  to  the 
examination  of  nicotin  solutions  and  tobacco  extracts  which  are  used 
in  the  official  dipping  of  sheep  and  cattle  for  scabies.  The  method 
presented  by  Mr.  Chapin  has  many  advantages  over  the  Kissling 
method  which  is  now  generally  employed,  and  it  is  believed  that  the 
paper  will  be  of  interest  and  value  not  only  to  Federal  and  State 
officers  who  have  to  deal  with  nicotin  solutions,  but  also  to  manu- 
facturers who  are  endeavoring  to  produce  standard  and  reliable 
articles. 

Respectfully,  A.  D.  MELVIN, 

Chief  of  Bureau. 
Hon.  JAMES  WILSON, 

Secretary  of  Agriculture. 

3 


CONTENTS. 


Page. 

Introductory 5 

The  Kissling  method ^ 6 

The  petroleum  ether  method 8 

The  nilicotungstate  method 10 

Development  of  the  quantitative  method 12 

Analytical  results  obtained  by  the  silicotungstate  method 14 

The  determination  of  nicotin  in  commercial  preparations 15 

The  effect  of  extraneous  bases 16 

Tests  on  a  rapid  modification  of  the  method 17 

The  steam  distillation  of  nicotin  preparations 20 

Summary  and  codified  directions  for  routine  work 21 

4 


THE  DETERMINATION  OF  N1COTIN  IN  NICOTIN 
SOLUTIONS  AND  TOBACCO  EXTRACTS. 


INTRODUCTORY. 

Nicotin  has  long  been  regarded  as  a  valuable  agent  for  the  ex- 
termination of  certain  species  of  insects  infesting  plants  and  animals. 
For  several  years  proprietary  nicotin  solutions  and  tobacco  extracts 
have  been  permitted  by  the  Bureau  of  Animal  Industry  1  for  use  in 
the  official  dipping  of  cattle  and  sheep  affected  with  or  exposed  to 
scabies.  Nicotin  baths  employed  in  official  dipping  are  required  to 
possess  a  minimum  strength  of  either  0.05  or  0.07  of  1  per  cent  of 
nicotin,  according  to  circumstances.  Upon  the  Biochemic  Division 
of  the  Bureau  of  Animal  Industry  has  accordingly  devolved  the 
task  of  examining  a  considerable  number  of  such  preparations,  in- 
cluding both  samples  from  manufacturers  who  have  desired  to  ob- 
tain permission  for  the  use  of  their  products  in  official  dipping,  and 
samples  of  dips  actually  put  to  such  use,  transmitted  by  bureau  in- 
spectors in  the  field. 

The  method  hitherto  employed  by  the  bureau  for  the  determina- 
tion of  nicotin  is  the  Kissling  method,  adopted  several  years  ago  by 
the  Association  of  Official  Agricultural  Chemists '  as  the  standard 
method  for  nicotin  in  tobacco  and  tobacco  products.  The  Kissling 
method  in  experienced  hands  and  in  the  absence  of  certain  inter- 
fering substances  unquestionably  yields  accurate  results.  But  it 
contains  a  number  of  pitfalls  fo'r  the  unwary;  it  is  cumbersome, 
tedious,  and  expensive.  The  bureau  is  now  in  possession  of  a  method 
which  appears  to  yield  results  of  a  higher  degree  of  accuracy  than 
the  classical  Kissling  method,  at  a  less  expenditure  of  time,  chem- 
icals, and  expensive  apparatus,  and  to  yield  such  results  in  the  hands 
of  any  competent  chemist  of  ordinary  training.  Therefore  this 
paper  is  offered  in  order  that  the  method  may  be  available  to  manu- 
facturers, who  are  naturally  interested  in  maintaining  their  prepara- 
tions for  use  in  official  dipping  at  the  standard  required  by  the 
bureau,  as  well  as  to  the  considerable  number  of  manufacturing,  State, 
and  Government  chemists  who  are  concerned  with  the  examination 

1  Bureau  Animal  Industry  Order  143,  Regulations  25  and  33,  and  Amendment  1. 

5 


6  DETERMINATION   OF   NICOTIN   IN   TOBACCO  EXTRACTS. 

of   nicotin    preparations   used    as   general    insecticides   upon    both 
animals  and  plants.1 

THE  KISSLING  METHOD. 

The  Kissling  method  as  adopted  by  the  Association  of  Official 
Agricultural  Chemists  is  carried  out  as  follows : 2 

Weigh  from  5  to  6  grams  of  tobacco  extract,  or  20  grams  of  finely  powdered 
tobacco,  which  has  been  previously  dried  at  60°  C.,  so  as  to  allow  it  to  be  pow- 
dered, into  a  small  beaker.  Add  10  c.  c.  of  the  alcohol-soda  solution  [6  grams 
NaOH,  40  c.  c.  wat'er,  60  c.  c.  of  90  per  cent  alcohol]  and  follow,  in  the  case  of 
the  tobacco  extract,  with  enough  chemically  pure  powdered  calcium  carbonate 
to  form  a  moist  but  not  lumpy  mass.  Mix  the  whole  thoroughly.  Transfer  this 
to  a  Soxhlet  extractor  and  exhaust  for  about  five  hours  with  ether.  Evaporate 
the  ether  at  a  low  temperature  by  holding  over  the  steam  bath,  and  take  up  the 
residue  with  50  c.  c.  of  the  dilute  sodium  hydroxid  solution  [4  grams  NaOH, 
1000  c.  c.  water].  Transfer  this  residue  by  means  of  water  to  a  Kjeldahl  flask, 
capable  of  holding  about  500  c.  c.,  and  distil  in  a  current  of  steam,  using  a  con- 
denser through  which  water  is  flowing  rapidly.  Use  a  three-bend  outflow  tube, 
a  few  pieces  of  pumice,  and  a  small  piece  of  paraffin,  to  prevent  bumping  and 
frothing.  Continue  the  distillation  until  all  the  nicotin  has  passed  over,  the  dis- 
tillate usually  varying  from  400  to  500  c.  c.  When  the  distillation  is  complete, 
only  about  15  c.  c.  of  the  liquid  should  remain  in  the  distillation  flask.  Titrate 
the  distillate  with  standard  sulphuric  acid,  using  phenacetolin  or  cochineal  as 
indicator.  One  molecule  of  sulphuric  acid  is  equivalent  to  two  molecules  of 
nicotin. 

The  Kissling  method  involves  two  series  of  operations,  (1)  extrac- 
tion with  ether,  (2)  distillation  with  steam  and  titration.  For  con- 
venience of  discussion  these  two  series  of  operations  will  be  con- 
sidered in  reverse  order. 

Titration  and  steam  distillation. — None  of  the  indicators  tried  in 
this  laboratory  have  given  perfect  satisfaction  in  the  titration  of  dis- 
tillates from  commercial  nicotin  preparations,  although  some  show  a 
sharp  enough  change  of  color  when  used  with  solutions  of  pure  nico- 
tin. In  practice,  as  noted  by  other  investigators,  the  end  point  is  apt 
to  be  rather  indefinite,  requiring  some  care  and  experience  on  the  part 
of  the  operator  if  accurate  results  are  to  be  obtained.  A  freshly  pre- 
pared alcoholic  solution  of  phenacetolin  has  yielded  the  best  results 
in  this  laboratory,  the  practice  here  having  been  to  distil  over  the 
nicotin  into  a  measured  amount  of  standard  sulphuric  acid,  and  to 
titrate  back  the  excess  of  acid. 

The  chief  drawback  to  the  operation,  however,  is  the  fact  that  it 
reckons  as  nicotin  all  alkaline  substances  which  may  gain  access  to 

1  In  the  Issue  of  the  Chemlker-Zeltung  of  January  10,  1011  (Jahrgang  XXXV,  nummcr 
4,  selte  30),  in  an  article  entitled  "  Zur  Bcstimmung  des  Nlcotins  In  konzentriertcn  Tabak- 
siifti-n,"  Dr.  Johannes  SchrOder  reviews  the  most  recent  work  published  upon  the  dntor- 
mlnatlon  of  nicotin,  notes  some  Inadequacies  In  methods  at  present  In  vogue  and  forcibly 
presents  the  pressing  need  for  a  method  which,  being  accurate,  practical,  and  universally 
employed,  shall  constitute  a  standard  method  for  the  valuation  of  a  class  of  preparations 
which,  according  to  flgures  cited,  are  employed  In  large  qnnntltles. 

1  U.  8.  Department  of  Agriculture,  Bureau  of  Chemistry  Bulletin  107,  Revised  1010. 


THE   KISSLING   METHOD.  7 

the  receiver  during  steam  distillation :  Alkali  extracted  from  the 
glass  condenser,  if  such  is  used;  alkali  entrained  by  the  current  of 
steam;  ammonia,  amins,  and  pyridin  bases,  if  such  were  present  in 
the  original  extract  and  not  removed  during  preceding  operations; 
ammonia  from  the  decomposition  of  proteid  matter  of  the  extract 
which  may  have  reached  the  distillation  flask ;  all  are  possible  sources 
of  error  which  may  cause  too  high  results  to  be  obtained.  Disregard- 
ing minor  sources  of  error,  it  is  certain  that  all  ammonia,  amins,  and 
pyridin  bases  must  be  eliminated  before  the  distillation  with  steam  is 
undertaken.  This  end  is  not  accomplished  by  the  evaporation  at  a 
low  temperature  over  the  steam  bath  directed  for  the  removal  of 
ether,  for  experiments  in  this  and  other  laboratories  have  shown  that 
such  evaporation  must  cease  while  there  is  still  a  considerable  quan- 
tity of  ether  remaining  over  the  alcoholic-aqueous  residue  in  the 
extraction  flask  or  loss  of  nicotin  will  occur. 

Extraction  with  ether. — From  the  preceding  it  is  clear  that  if 
volatile  alkalis  other  than  nicotin  are  to  be  eliminated  at  all  during 
the  Kissling  process  it  must  be  during  the  operation  of  extraction 
with  ether.  That  such  is  actually  the  case  may  be  plainly  shown  by 
a  slip  of  litmus  paper  inserted  in  the  top  of  the  condenser  during 
extraction.  The  official  directions  of  the  Association  of  Official 
Agricultural  Chemists  prescribe  an  extraction  time  of  five  hours, 
which  period  is  undoubtedly  sufficient  to  extract  all  the  nicotin.  It 
is  not,  however,  in  many  cases  nearly  long  enough  to  volatilize  all 
ammonia  and  amins,  particularly  if  the  condenser  used  is  of  the 
spiral  form  from  which  evolved  vapors  can  not  find  a  ready  escape. 
The  process  of  extraction  must  be  continued  until  a  strip  of  red 
litmus  paper  inserted  in  the  upper  end  of  the  condenser  retains  its 
color  permanently.  The  length  of  time  required  for  such  a  complete 
elimination  of  extraneous  volatile  bases  is  naturally  very  variable, 
but  an  extraction  period  of  more  than  15  hours  has  sometimes  proved 
necessary  in  this  laboratory.  It  is  to  be  noted  that  in  this  way  only 
ammonia  and  amins  are  eliminated.  Pyridin  bases,  on  account  of 
their  high  boiling  points  and  great  solubility  in  ether,  remain  behind 
with  the  nicotin. 

The  Kissling  method,  therefore,  may  yield  accurate  results,  but 
it  yields  them  only  in  the  absence  of  certain  interfering  substances 
and  only  in  the  hands  of  a  chemist  of  special  experience.  It  is, 
moreover,  highly  probable  that  in  the  case  of  commercial  nicotin 
preparations  the  apparently  accurate  results  obtained  are  in  reality 
simply  a  nice  balancing  of  errors.  In  the  necessary  manipulation  and 
during  the  long  period  of  extraction  often  required,  a  considerable 
amount  of  ether  is  lost.  Bertrand  and  Javilier  state  that  their  experi- 
ments show  that  in  the  distillation  of  ethereal  solutions  of  nicotin,  be- 
tween 1  and  2  milligrams  of  the  alkaloid  accompany  each  100  c.  c.  of 


8  DETERMINATION   OF   NICOTIN   IN   TOBACCO   EXTRACTS. 

ether  distilled,  the  loss  becoming  still  more  notable  in  the  case  of 
fairly  concentrated  solutions.  In  a  properly  executed  determination 
by  the  Kissling  method  the  inevitable  loss  of  small  amounts  of  nicotin 
is  probably  fairly  well  balanced  by  the  equally  inevitable  retention  of 
small  amounts  of  ammonia  and  amins. 

Aside  from  the  question  of  accuracy,  other  factors,  such  as  the 
amount  of  personal  attention  required,  the  employment  of  expensive 
apparatus,  and  the  considerable  loss  of  ether  which  inevitably  occurs, 
contribute  to  make  the  process  an  expensive  one,  particularly  when 
in  view  of  the  rather  loose  agreement  between  check  determinations 
four  or  five  repetitions  may  be  necessary  in  order  to  obtain  a  thor- 
oughly substantiated  result. 

THE  PETBOLEUM  ETHER  METHOD. 

About  10  years  ago  Toth1  employed  a  method  for  the  determina- 
tion of  nicotin  in  tobacco,  which  appeared  to  give  good  results.  The 
tobacco  leaves  were  rubbed  up  in  a  porcelain  mortar  with  a  small 
quantity  of  strong  caustic-soda  solution,  then  thoroughly  incorpo- 
rated with  plaster  of  Paris  until  a  dry  powder  resulted.  The  latter 
was  brought  into  a  stoppered  glass  cylinder  and  thoroughly  shaken 
with  a  definite  volume  of  a  mixture  of  petroleum  ether  and  ethyl 
ether.  After  subsidence  an  aliquot  of  the  ether  was  pipetted  out, 
treated  with  indicator  and  excess  of  standard  acid,  and  finally 
titrated  back  with  standard  alkali.  Toth  found  that  when  ammo- 
nium salts  were  present  only  a  very  little  ammonia  was  dissolved 
by  the  ether,  and  that  the  trace  so  dissolved  could  be  readily  re- 
moved by  blowing  air  through  the  ether  for  a  short  time,  though 
with  some  danger  of  simultaneous  loss  of  nicotin. 

In  searching  for  an  improvement  on  the  Kissling  method  first  at- 
tempts were  directed  toward  a  modification  of  Toth's  method  along 
the  following  lines: 

To  a  weighed  amount  of  nicotin  solution  or  tobacco  extract  was 
added  about  4  c.  c.  of  kerosene,  followed  by  a  few  grams  of  calcium 
hydrate  or  a  very  few  cubic  centimeters  of  a  nearly  saturated  caustic 
soda  solution.  After  thorough  mixing,  plaster  of  Paris,  previously 
moistened  with  kerosene,  was  added  in  liberal  excess  of  the  quantity 
needed  to  combine  with  all  water  present,  and  the  mass  was  mixed 
to  uniform  consistency.  During  the  process  of  dehydration  the 
kerosene  previously  added  would  presumably  act  as  a  solvent  for 
liberated  nicotin  and  so  prevent  loss  by  volatilization.  The  mixture 
was  then  transferred  to  the  capsule  of  a  Soxhlet  apparatus  and  ex- 
tracted with  petroleum  ether.  On  account  of  the  total  absence  of 

1  Tuth.  Julius  NI-IIP  Mrthndp  znr  I'-.-st immnnir  d<»8  NIcotlns  Im  Tnbnk  nnd  In  den 
wlMerigen  AusiUgen  der  Tabakbltttter.  Chemlker-Zeltung,  Jahrgang  25,  No.  57,  p.  610, 
July  17,  1001. 


THE   PETROLEUM    ETHER    METHOD. 


water  and  the  slight  degree  of  solubility  of  ammonia  and  amins  in 
petroleum  ether,  these  substances  were  rapidly  evolved  from  the  top 
of  the  condenser,  and  a  slip  of  red  litmus  paper  placed  therein  re- 
tained its  color  after  a  very  much  shorter  period  of  extraction  than  is 
required  in  the  Kissling  method. 

The  petroleum  ether  extract  remaining  in  the  extraction  flask  was 
transferred  to  a  separatory  funnel  and  shaken  out  with  a  measured 
quantity  of  standard  acid,  followed  by  two  or  three  washings  of 
water.  The  excess  of  acid  in  the  whole  aqueous  extract  was  lastly 
titrated  back  with  standard  alkali,  following  the  method  formerly 
used  by  Loesch. 

The  following  table  will  illustrate  the  character  of  the  results 
obtainable  by  this  method : 

TABLE  1. — Comparative  results  of  Kissling  and  petroleum  ether  methods  on 
commercial  nicotin  solutions  and  tobacco  extracts. 


Character  of  material. 

Kissling 
method. 

Petroleum 
ether 
method. 

Tobacco  extract,  No.  754  .                   .         ....                    .             .         .  .... 

2.92 
2.88 

2.98 
2.92 

2.96 

Nicotin  solution,  No.  755  

39.80 
40.03 

39.80 
40.45 

40.75 

Nicotin  solution,  No.  810  

38.89 
39.54 

40.51 
40.08 

39.42 

Tobacco  extract,  No.  834  

2.91 
2.84 

2.98 
2.88 

3.03 

Nicotin  solution,  No.  835  

141.40 
40.84 

40.70 
40.91 

40.29 

Nicotin  solution,  No.  841  

f          40.29 

40.49 

The  method  appears,  therefore,  to  yield  results  which  check  very 
well  with  those  obtained  by  the  Kissling  method.  Its  positive  advan- 
tages are  (1)  much  saving  of  time  and  expense  by  the  replacement  of 
a  long  period  of  extraction  with  ethyl  ether  by  a  short  period  with 
petroleum  ether,  and  (2)  elimination  of  the  operation  of  steam  dis- 
tillation. But  the  proper  preparation  of  the  sample  for  extraction 
requires  considerable  manipulation,  and  the  method  is  still  a  volumet- 
ric one,  involving  the  use  of  a  somewhat  indefinite  end  point.  More- 
over, the  presence  of  pyridin  bases  will  lead  to  false  results  exactly 
as  in  the  case  of  the  Kissling  method,  and  in  addition  a  new  source 
of  error  resulting  from  the  possible  presence  of  certain  nonvolatile 
alkaloids  is  introduced.  Hence  the  method  described  has  been  but 
little  used  in  practice. 

Incidentally  Table  1  may  serve  to  illustrate  the  rather  wide  varia- 
tion between  check  determinations  by  the  Kissling  method  when 
76687°— Bull.  133—11 2 


10  DETERMINATION    OF   NICOTIN   IN   TOBACCO   EXTRACTS. 

applied  to  commercial  preparations.  A  difference  in  duplicate  results 
of  1  per  cent  of  the  amount  of  nicotin  operated  upon  must  be  ex- 
pected to  occur  regularly  in  routine  work,  while  a  difference  of  2  per 
cent  is  not  unusual. 

THE  SILICOTUNGSTATE  METHOD. 

In  1909  Bertrand  and  Javillier1  published  a  paper  on  the  use  of 
silicotungstic  acid  as  an  aid  in  the  quantitative  determination  of 
nicotin,  employing  it  in  the  examination  of  tobacco.  The  first  steps 
•in  their  method  were  to  extract  nicotin  by  boiling  the  tobacco  leaves 
with  dilute  hydrochloric  acid,  then  to  precipitate  the  nicotin  by  the 
addition  of  silicotungstic  acid.  The  precipitate  of  nicotin  silicotung- 
state,  after  washing,  was  brought  into  a  flask,  and  the  nicotin,  liber- 
ated by  an  addition  of  calcined  magnesia,  was  distilled  over  with 
steam,  and  determined  in  the  distillate  by  titration  with  standard 
acid. 

The  method  resembles  the  Kissling  method  to  the  extent  that  the 
nicotin  is  finally  determined  by  titration  after  distillation  with 
steam,  and  accordingly  it  is  subject  to  several  similar  possible  inaccu- 
racies. It  successfully  eliminates  the  effect  of  ammonia  present  as 
such  or  as  ammonium  salts,  for  ammonium  silicotungstate  is  soluble 
in  water.  But  silicotungstic  acid,  like  some  other  reagents  for  alka- 
loids, is  also  a  precipitant  for  proteids,  and  hence  the  nicotin  silico- 
tungstate, when  brought  into  the  flask  for  steam  distillation,  may  be 
largely  contaminated  with  proteid  matter.  It  is  well  known  that 
proteid  matter  when  distilled  with  steam  at  atmospheric  pressure  and 
in  the  presence  of  caustic  alkalies  may  yield  notable  quantities  of 
ammonia.  The  authors  therefore  employ  calcined  magnesia  at  this 
stage  of  their  process. 

It  is  true  that  magnesia  has  in  the  past  received  considerable 
recognition  as  the  alkali  to  be  employed  when  preexisting  ammonia 
in  organic  matter  is  to  be  determined.  In  but  comparatively  few 
cases,  however,  has  it  yielded  results  above  suspicion,  a*nd  among 
chemists  of  the  present  day  it  appears  quite  generally  recognized  that 
proteid  matter  in  general  is  subject  to  a  certain  amount  of  decom- 
position when  distilled  with  magnesium  oxid  at  atmospheric  pres- 
sure, so  that  the  substance  is  employed  in  such  circumstances  only 
provisionally  for  lack  of  a  more  convenient  method,  or  when  results 
of  a  comparative,  rather  than  of  an  absolute,  degree  of  accuracy  are 
required. 

On  the  whole,  then,  the  method  as  employed  by  Bertrand  and 
Javillier  did  not  appear  to  embody  everything  desired  by  the  bureau 

1  Bertrand,  G.,  and  Javillier,  M.  Bur  le  slllcotungstnte  dc  nicotine  et  sur  le  dosage  do 
cet  alrololde.  Bulletin  des  Sciences  Pharmacologlques,  tome  10,  No.  1,  pp.  7-14,  Jan., 

JIM/.' 


THE   SILICOTUNGSTATE   METHOD.  11 

in  a  method  worthy  to  replace  the  Kissling  method,  when  applied  to 
the  examination  of  commercial  nicotin  preparations. 

At  the  conclusion  of  their  paper  Bertrand  and  Javillier  append 
the  statement  that  in  place  of  the  volumetric  method,  which  they 
prefer  on  account  of  its  greater  convenience,  one  may  substitute  a 
gravimetric  method,  in  which  the  distilled  nicotin  is  again  precipi- 
tated with  silicotungstic  acid,  the  precipitate  filtered,  washed,  and 
finally  ignited.  From  the  residue  of  SiO2  and  WO3  may  be  calculated 
the  weight  of  nicotin  originallj7  present.  The  authors  quote  no  ex- 
perimental work  to  show  that  this  process  is  of  more  than  theoretical 
applicability;  nevertheless  it  appeared  plausible  and  well  worth  in- 
vestigating. Preliminary  experiments  afforded  encouraging  results, 
and  a  thorough  study  of  the  matter  was  undertaken. 

Silicotungstic  acid  is  a  white  to  yellowish-white  crystalline  sub- 
stance, presumably  of  the  formula  4H2O  •  SiO2  •  12  WO3  +  22H2O. 
When  ignited  it  should  leave,  therefore,  85.87  per  cent  of  a  residue 
consisting  of  SiO2  and  WO3.  Ignition  of  1.5397  grams  of  the  ma- 
terial employed  in  this  laboratory  gave  a  residue  of  1.3981  grams, 
equal  to  90.08  per  cent.  The  acid  itself,  and  its  salts  with  the  alkalis 
and  ammonia,  are  readily  soluble  in  acidulated  water. 

According  to  Bertrand  and  Javillier,  nicotin  silicotungstate  dried 
at  a  temperature  of  30°  C.  is  a  rose-white  salt  of  the  formula 
2C10H14N2  •  2H2O  •  SiO2  •  12WO3  +  5H2O,  which  loses  its  five  mole- 
cules of  water  of  crystallization  when  maintained  for  an  hour  at 
120°  C.  The  solubility  of  the  hydrated  salt  in  water  has  not  been 
definitely  determined,  and,  at  any  rate,  it  is  very  probably  affected 
somewhat  by  the  presence  of  acids  and  salts.  The  above  authors, 
however,  cite  the  limits  at  which  a  solution  of  the  acid  may  serve 
as  a  qualitative  test  for  nicotin.  At  a  dilution  of  1  in  300.000  of 
nicotin  in  the  presence  of  one-tenth  of  1  per  cent  concentrated  hydro- 
chloric acid,  an  almost  immediate  opalescence  follows  the  addition 
of  the  reagent;  less  or  more  acid  prevents  an  immediate  visible  re- 
action, though  at  1  in  200,000  it  appears  in  presence  of  four-tenths 
of  1  per  cent  of  acid.  These  limits,  however,  are  far  from  marking 
the  true  solubility  of  the  salt,  for  at  considerably  greater  dilutions 
and  in  presence  of  much  more  acid  it  will  deposit  on  standing,  not 
then  as  a  cloud  or  an  opalescence,  but  in  definite  crystalline  form. 
The  above-mentioned  authors  have  obtained  such  crystals  at  a  dilu- 
tion of  1  in  1,000,000,  but  have  not  pushed  their  investigations  farther. 

Silicotungstic  acid  does  not  form  such  insoluble  precipitates  with 
all  alkaloids,  as  indicated  by  recent  work  of  Javillier.1  Conin,  for 
example,  which  is  of  interest  in  this  connection  for  the  reason  that, 
like  nicotin,  it  is  volatile  with  steam,  yields  no  precipitate  with  sili- 
cotungstic acid  at  dilutions  greater  than  1  in  5,000. 

1  Javillier,  M.  Sur  les  silicotungstates  de  conlclne,  de  sparte'lne  et  d'atropine.  Bulletin 
des  Sciences  Pharmacologiques,  tome  17,  No.  6,  pp.  315-320,  June,  1910. 


12  DETERMINATION   OF   NICOTIN   IN   TOBACCO  EXTRACTS. 

In  the  case  of  some  alkaloidal  reagents,  such  as  picric  acid,  a  con- 
siderable quantity  of  the  reagent  must  be  present  before  any  reaction 
is  evident.  Such  appears  not  to  be  true  of  silicotungstic  acid,  for  the 
present  writer  found  that  a  1  in  10,000  solution  in  one-tenth  per  cent 
hydrochloric  acid  yields  an  immediate  opalescence  upon  the  addition 
of  one  drop  of  a  two-tenths  per  cent  nicotin  solution,  increased  to 
a  heavy  turbidity  upon  the  addition  of  more  nicotin.  Hence  nicotin 
is  an  appropriate  reagent  for  the  qualitative  detection  of  small  quan- 
tities of  silicotungstic  acid. 

DEVELOPMENT  OF  THE  QUANTITATIVE  METHOD. 

From  the  above  observations  it  is  evident  that  in  quantitative  work 
nicotin  silicotungstate  should  be  precipitated  from  a  solution  contain- 
ing not  less  than  one-tenth  of  1  per  cent  of  concentrated  hydrochloric 
acid ;  that  the  precipitate  should  be  allowed  to  stand  before  filtration 
until  it  has  changed  to  a  crystalline  form ;  that  the  precipitate  dur- 
ing filtration  should  be  washed  with  water  containing  one-tenth  of 
1  per  cent  concentrated  hydrochloric  acid,  and  washing  continued 
until  the  filtrate  shows  no  opalescence  when  treated  with  a  few  drops 
of  a  dilute  nicotin  solution. 

Since  ammonia  and  amins  are  not  precipitated  by  silicotungstic 
acid,  the  first  step  in  a  quantitative  method  for  the  determination  of 
nicotin  appeared  to  be  the  distillation  of  the  solution  or  extract  in  a 
current  of  steam  after  addition  of  caustic  soda.  An  aliquot  of  the 
distillate  might  then  be  precipitated  with  silicotungstic  acid,  and 
filtered  and  washed  with  the  precautions  noted  above.  The  pre- 
cipitate might  then  be  ignited  and  the  residue  of  SiO2  and  WO3 
weighed  as  suggested  by  Bertrand  and  Javillier,  or  the  filtration 
might  be  performed  in  a  Gooch  crucible  and  the  salt  directly 
weighed  after  drying  at  120°  C.  Both  methods  were  tried. 

Weighing  as  anhydride. — The  anhydrid  method  is  obviously  the 
quicker  and  easier  of  the  two  possibilities.  A  platinum  crucible  is 
naturally  employed,  from  which  the  residue  is  easily  removed.  One 
drawback  to  the  method  results  from  the  fact  that  when  nicotin 
silicotungstate  is  decomposed  by  heat  much  carbon  is  deposited 
throughout  the  residual  mass.  If  the  ignition  is  performed  care- 
fully and  with  free  access  of  air,  such  deposited  carbon  appears  to 
be  readily  and  completely  burned  away.  The  conditions  are,  how- 
ever, evidently  very  favorable  for  the  retention  of  unburned  carbon 
or  the  reduction  of  WO3  within  the  interior  of  the  residue,  which 
forms  a  coherent  porous  mass.  Moreover,  WO3  is  recognized  to  be 
appreciably  volatile  at  a  high  temperature,  hence  protracted  ignition 
of  the  residue  must  be  avoided,  though  a  high  enough  temperature 
must  be  reached  to  assure  dehydration  of  silicic  acid.  Citation 
of  an  experiment  performed  will  best  serve  to  show  the  difficulties 
here  involved.  The  precipitate  obtained  from  about  0.06  gram  of 


THE   SILICOTUNGSTATE   METHOD.  13 

nicotin  was  filtered  on  paper,  washed,  and  the  wet  paper  and  precip- 
itate brought  into  a  platinum  crucible.  After  drying  and  carbon- 
ization over  a  Bunsen  burner  the  crucible  was  inclined  and  carbon 
burned  away  at  a  gradually  increased  heat.  After  cooling  and 
weighing,  the  crucible  and  contents  were  next  subjected  to  successive 
periods  of  heating,  and  were  weighed  after  each  period.  The  re- 
sults are  shown  in  Table  2. 

TABLE  2. — Effect  of  continued  ignition  upon  the  residue  of  anhydrids  from 

nicotin  silicotungstate. 


Method  of  Ignition. 


Weight  of 

crucible  and 

residue. 


After  ignition  over  Bunsen  burner 

After  5  additional  minutes  over  Bunsen  burner. 
After  5  additional  minutes  over  Teclu  burner. . . 


Do. 
Do. 
Do. 


After  20  to  25  additional  minutes  over  Teclu  burner. 
After  5  additional  minutes  over  blast  lamp 


Grams. 
20.5029 
20.5024 
20.  5018 
20.  5015 
20.5015 
20.5012 
20.5000 
20.4997 


NOTE. — The  crucible  itself  lost  0.0004  gram  during  the  experiment. 

It  is  evident  that  the  weight  of  the  residue  changes  appreciably 
on  ignition,  the  degree  and  rate — and  even  the  direction — of  the 
change  depending  naturally  on  such  circumstances  as  the  conditions 
of  heating  and  the  degree  of  porosity  of  the  residue.  The  results  of 
Table  2  indicate  that  heating  over  a  Teclu  burner  for  a  period  be- 
tween five  and  ten  minutes  will  give  the  most  consistent  results  in 
practice.  The  residue  forms  a  porous  mass,  usually  a  clear  lemon- 
yellow  on  the  outside  but  showing  a  decided  greenish  hue  in  the 
interior. 

Weighing  as  salt. — The  salt  method  is  subject  to  three  disadvan- 
tages when  compared  to  the  anhydrid  method:  (1)  A  Gooch  crucible 
must  be  prepared  and  weighed  for  each  determination;  (2)  the  pre- 
cipitate packs  down  tightly  upon  the  felt  under  suction,  so  that  fil- 
tration is  slow;  (3)  the  anhydrous  salt  is  very  hygroscopic — a  fact 
not  mentioned  by  Bertrand  and  Javillier — hence  the  crucible  and 
contents,  after  drying,  must  be  tightly  inclosed  in  a  weighing  bottle 
during  cooling  and  weighing.  On  the  other  hand,  results  obtained 
by  the  salt  method  are  free  from  the  special  sources  of  error  attached 
to  the  anhydrid  method.  The  salt  reaches  constant  weight  at  120°  C. 
and  may  be  held  at  130°  C.  without  showing  further  loss.1  Hence 
the  method  is  of  value  as  an  ultimate  reference  method  in  cases  where 
very  exact  and  indubitable  results  are  necessary.  For  ordinary  pur- 
poses the  anhydrid  method  appears  sufficiently  accurate  and  is  cer- 
tainly much  more  rapid  and  convenient. 

1  The  anhydrous  salt  theoretically  contains  10.12  per  cent  nicotin.  Before  weighing  the 
salt  and  Gooch  crucible  inclosed  in  the  weighing  bottle,  the  stopper  of  the  latter  must  be 
loosened  for  an  Instant  to  permit  equalization  of  air  pressure. 


14 


DETERMINATION   OF   NICOTIN   IN   TOBACCO  EXTRACTS. 


ANALYTICAL  RESULTS  OBTAINED  BY  THE  SILICOTUNGSTATE   METHOD. 

Thesilicotungstate  method  was  first  tested  upon  solutions  of  nicotin. 
The  material  bore  the  designation  "  highest  purity  "  over  the  name  of 
a  firm  of  excellent  reputation.  That  it  was  not  absolutely  pure  was 
indicated  by  an  evident  opalescence  when  it  was  dissolved  in  dilute 
hydrochloric  acid.  A  gram  or  two  was  weighed  in  a  stoppered 
weighing  bottle,  washed  into  a  measuring  flask  with  slightly  acidu- 
lated water,  and  made  to  volume.  For  the  determination  an  aliquot 
was  pipetted  out,  made  to  about  50  c.  c.,  and  sufficient  dilute  hydro- 
chloric acid  added  to  bring  the  amount  present  to  between  two-tenths 
and  four-tenths  of  1  per  cent  of  concentrated  hydrochloric  acid.  To 
the  fluid  so  prepared  was  next  added  some  excess  of  a  silicotungstic 
acid  solution,  and  the  whole  was  well  stirred  and  allowed  to  stand 
until  the  next  day.  By  that  time  the  precipitates,  at  first  finely 
divided  and  settling  very  slowly,  had  become  a  mass  of  detached 
glittering  crystals,  settling  quickly  when  agitated.  The  precipitate 
was  filtered  and  washed  with  water  containing  1  c.  c.  of  concentrated 
hydrochloric  acid  in  a  liter,  and  then  treated  according  to  one  or  the 
other  of  the  two  methods  outlined  above.  The  results  are  given  in 
the  following  table : 

TABLE   3. — Determination   by  silicotungstate  method   of  nicotin   in   "  Wicotin, 

highest  purity." 


Weight  of 
nicotin 
taken. 

Weight  of 
anhydrous 
salt. 

Weight  of 
anhydrids. 

Per  cent 
nicotin. 

Solution  A      

Gram. 
0.05856 

Gram. 

Gram. 
0.  5103 

99.34 

.05856 

.5119 

99.65 

.05856 

0.  5761 

99.56 

.05856 

.5756 

99.47 

.05856 

.5777 

99.83 

.11712 

1.1505 

99.42 

Solution  B  

.05506 

.5405 

99.34 

The  results  of  the  foregoing  table  do  not  justly  show  the  precise 
limits  within  which  duplicate  determinations  upon  a  single  nicotin 
solution  may  be  made  to  check,  for  in  the  work  no  special  precau- 
tions were  taken  outside  of  ordinary  laboratory  practice.  In  taking 
aliquots  of  the  nicotin  solution  the  ordinary  25  c.  c.  pipettes  supplied 
to  the  laboratory  were  employed  indifferently,  as  they  happened  to 
come  to  hand  on  different  days.  These  pipettes,  though  supplied  by 
reputable  makers,  were  not  calibrated,  and  a  subsequent  test  of  some 
of  the  stock  in  hand  showed  that  the  variation  in  volumes  delivered 
was  nearly  of  as  great  magnitude  as  the  variation  in  the  percentages 
of  nicotin  found  in  the  samples. 

In  the  above  series  of  determinations  the  volume  of  filtrate  and 
washings  was  not  definitely  noted,  though  it  evidently  averaged  about 


THE   SILICOTUNGSTATE   METHOD. 


15 


150  c.  c.  To  determine  whether  any  restriction  of  or  correction  for 
the  volume  of  filtrate  and  washings  might  be  necessary,  an  aliquot  of 
Solution  A  containing  0.05856  gram  nicotin  was  precipitated  and 
filtered  as  before  upon  an  S.  &  S.  No.  589  filter  paper,  9  cm.  in  diame- 
ter, and  washed  in  the  ordinary  manner  until  the  total  volume  of 
filtered  liquid  amounted  to  500  c.  c.  The  weight  of  residue  obtained 
after  ignition  was  0.5116  gram,  equivalent  to  99.59  per  cent  nicotin. 
A  repetition  of  the  experiment,  continuing  washing  until  the  total 
volume  amounted  to  900  c.  c.,  gave  0.5120  gram  residue,  equivalent  to 
99.67  per  cent  nicotin.  It  is  hence  apparent  that  the  precipitate  is 
extremely  insoluble,  that  it  may  be  precipitated  quantitatively  from 
very  dilute  solution,  and  that  no  correction  for  volume  of  filtrate  or 
washings  is  necessary. 

THE  DETERMINATION  OF  NICOTIN  IN   COMMERCIAL  PREPARATIONS. 

If  the  silicotungstate  method  is  destined  to  receive  recognition  and 
wide  employment  as  a  reliable  and  useful  method  for  the  determina- 
tion of  nicotin,  a  matter  of  considerable  practical  importance  will  be 
a  determination  of  the  degree  of  closeness  with  which  results  there- 
by obtained  may  be  expected  to  check  with  those  of  the  Kissling 
method  when  both  methods  are  applied  to  the  same  commercial  nico- 
tin preparations.  Several  such  preparations,  which  had  previously 
been  carefully  and  repeatedly  analyzed  by  the  Kissling  method,  were 
examined.  The  results  are  contained  in  the  following  table.  It  must 
be  noted  that  each  figure  given  in  the  last  two  columns  of  the  table 
under  the  "  silicotungstate  method  "  represents  a  single  complete  in- 
dependent analysis.  The  results  in  these  two  columns,  then,  are  com- 
parable as  complete  duplicates,  and  not  merely  as  duplicate  deter- 
minations upon  a  single  nicotin  distillate. 

TABLE  4. — Comparative  results  obtained  &j/  Kissling  and  silicotungstate  methods 
when  applied  to  commercial  nicotin  preparations. 


Character  of  preparation. 

Per  cent  nicotin. 

Kissling 
method 
(mean 
result). 

Silicotungstate  method. 

Weighed 
as  salt. 

Weighed 
as 
anhydrids. 

Nicotin  dip,  No.  660      

21.88 

21.91 

39.77 
39.84 

\      40.05 

8.32 

Nicotin  solution  No  810 

8.38 

8.35 
40.12 
40.00 
2.92 
2.93 

39.41 

2.94 

16  DETERMINATION   OF   NICOTIN   IN   TOBACCO   EXTRACTS. 

In  view  of  the  distinctly  different  rationale  of  the  two  methods 
and  the  difference  in  the  sources  of  possible  error  inherent  in  each, 
the  above  series  of  results  show  a  rather  surprising  agreement.  Ap- 
parently the  results  obtained  by  one  method  are  about  equally  likely 
to  be  either  higher  or  lower  than  the  results  obtained  by  the  other. 

THE  EFFECT  OF  EXTRANEOUS  BASES. 

As  already  noted,  ammonia  and  amins — but  not  pyridin — may  be 
practically  eliminated  by  the  Kissling  method  if  a  sufficiently  long 
period  of  extraction  is  employed.  Up  to  the  present  time  apparently 
the  only  attention  paid  to  the  possible  presence  of  pyridin  bases  in 
nicotin  solutions  is  contained  in  the  work  of  Emery,1  performed  in 
the  laboratories  of  this  bureau  some  years  ago.  Nicotin  is  levo- 
gyratory,  and  Emery  took  advantage  of  this  fact  to  work  out 
a  method  for  the  polariscopic  examination  of  nicotin  distillates. 
Emery's  method  is  not  particularly  accurate  when  considered  as  a 
method  for  the  determination  of  nicotin,  and  the  presence  of  pyridin 
bases  can  be  inferred  with  assurance  only  if  the  amount  of  nicotin 
so  found  is  notably  lower  than  that  obtained  by  the  Kissling  method. 

Ammonia  and  amins,  so  far  as  known,  are  not  precipitated  by 
silicotungstic  acid,  nor  are  the  anilins,  as  indicated  by  a  test  on  a 
solution  of  anilin  oil  in  dilute  hydrochloric  acid.  Pure  pyridin  in 
slightly  acid  solution  yielded  a  precipitate  with  silicotungstic  acid 
at  a  dilution  of  1  in  5,000  only  when  allowed  to  stand  several  hours ; 
at  a  dilution  of  1  in  10,000  no  precipitate  could  be  perceived  after 
forty-eight  hours.  Pyridin  bases  from  coal-tar  creosote  extracted  in 
the  laboratory  proved  to  yield  much  less  soluble  precipitates,  an 
immediate  opalescence  appearing  upon  the  addition  of  silicotungstic 
acid  to  a  solution  of  the  bases  containing,  roughly,  1  part  in  50,000, 
but  no  reaction  could  be  observed  at  a  dilution  of  1  in  100,000.  The 
precipitate  formed  from  the  higher  pyridin  bases  was  markedly 
different  in  appearance  from  nicotin  silicotungstate,  seeming  to  re- 
main amorphous,  and  yielding  a  permanently  cloudy  fluid.  It  is 
therefore  evident  that  the  silicotungstate  method  can  not  be  relied 
upon  to  eliminate  more  than  small  amounts  of  pyridin  bases.  It  will, 
however,  successfully  detect  such  bases  if  present  in  quantity  suffi- 
cient to  introduce  error  in  the  determination  of  nicotin,  for  although 
the  silicotungstates  of  some  of  the  pyridin  bases  are  difficulty  soluble, 
they  are  much  more  soluble  than  nicotin  silicotungstate;  hence,  if 
they  are  thrown  on  a  filter  and  washed,  the  washings  will  long  con- 
tinue to  yield  a  turbidity  when  tested  with  a  dilute  nicotin  solution, 
exactly  as  would  a  very  dilute  solution  of  silicotungstic  acid.  To 
illustrate  this  point,  0.01  gram  of  the  pyridin  bases  extracted  from 
coal-tar  creosote  was  completely  precipitated  from  50  c.  c.  of  slightly 

1  Emery,  James  A.  Estimation  of  nicotine  in  presence  of  pyrldine.  Journal  of  the 
American  Chemical  Society,  vol.  20,  No.  9,  pp.  1113-1119,  September,  1904.  __..  - 


THE   SILICOTUNGSTATE   METHOD. 


17 


acidulated  solution  with  silicotungstic  acid,  and  the  precipitate 
brought  on  a  filter  and  washed.  When  the  volume  of  filtrate  and 
washings  amounted  to  over  500  c.  c.  fresh  washings  still  yielded  a 
faint  but  unmistakable  opalescence  when  tested  Avith  a  few  drops  of 
nicotin  solution.  The  precipitate  had  then  been  reduced  to  a  very 
small  amount  in  the  point  of  the  filter  and  the  experiment  was 
discontinued. 

Accordingly,  it  appears  that  the  presence  of  pyridin  bases  in 
quantity  sufficient  to  affect  the  accuracy  of  the  determination  of  nico- 
tin in  commercial  preparations  will  be  betrayed  by  an  apparent  diffi- 
culty experienced  in  washing  the  precipitate  free  from  excess  of 
silicotungstic  acid. 

TESTS  ON  A  RAPID  MODIFICATION  OF  THE  METHOD. 

In  ordinary  work  the  natural  system  of  routine  will  be  to  perform 
the  steam  distillation  and  precipitation  on  one  day,  leaving  the  pre- 
cipitate to  form  and  settle  overnight.  In  exceptional  cases,  such  as 
certain  exigencies  of  factory  control  work,  even  so  much  delay  may 
cause  inconvenience.  Hence  an  attempt  was  made  to  hasten  the  con- 
version of  the  precipitate  into  a  filterable  form. 

A  study  was  first  made  of  the  effect  of  various  concentrations  of 
hydrochloric  acid  and  of  various  temperatures.  The  material  em- 
ployed was  another  sample  of  "  pure  nicotin  "  (sample  C),  evidently 
not  so  pure  as  those  previously  used.  To  about  1  gram  of  the  mate- 
rial was  added  5  c.  c.  of  dilute  hydrochloric  acid  (1  to  4)  and  the 
whole  was  made  to  500  c.  c.  with  distilled  water.  Portions  of  50  c.  c. 
were  drawn  with  the  same  pipette  for  all  determinations,  and  after 
dilution  to  100  c.  c.  were  acidified  and  precipitated  with  10  c.  c.  of  a 
12  per  cent  solution  of  silicotungstic  acid.  The  conditions  of  precipi- 
tation and  the  results  obtained  are  given  in  the  following  table : 

TABLE  5. — Tests  on  rapid  method  of  precipitation. 


No.  of 
test. 

Conditions  of  precipitation. 

Weight 
of  sam- 
ple. 

Weight 
of  anhy- 
drids. 

Nicotin. 

1 

Added  1  c.  c.  dilute  HC1;  stood  21  hours  at  21°  to  24°  C.  (recording 
thermometer)'  faintly  cloudy  when  filtered  

Gram. 
0.1034 

Oram. 
0.8815 

Per  cent. 
97.23 

2 

Added  2  c  c  dilute  HC1*  otherwise  as  above                            .... 

.1034 

.8824 

97.33 

3 

Added  5  c  c  dilute  HC1;  otherwise  as  above  

.1034 

.8825 

97.34 

4 

Added  10  c  c  dilute  HC1;  otherwise  as  above         

.1034 

.8834 

97.44 

5 

.1034 

.8802 

97.09 

6 
7 

Added  2  c.  c.  dilute  HC1;  stood  about  18  hours  at  about  30°  C  
Added  1  c.  c.  dilute  HC1;  stood  3  hours  at  37.5°  C.,  then  in  cold 
water  for  15  minutes  

.1047 
.1034 

.8943 
.8809 

97.34 
97.17 

8 

Added  10  c  c  dilute  HC1;  otherwise  as  No.  7  

.1034 

.8809 

97.17 

9 

Added2c.  c.  dilute  HC1;  on  steam  bath  20  minutes;  in  cold  water 
15  minutes                           .        

.1047 

.8900 

96.87 

10 

Added  2  c.  c.  dilute  HC1;  on  steam  bath  1  hour;  in  cold  water  15 
minutes  

.1047 

.8891 

96.78 

11 

Added  1  c.  c.  dilute  HC1;  on  steam  bath  2  hours;  in  cold  water  15 
minutes                                                       .  

.1047 

.8889 

96.76 

12 

Added  2  c.  c.  dilute  HC1;  on  steam  bath  J  hour;  at  room  tempera- 
ture 1  J  hours                       

.1034 

.8776 

96.80 

18 


DETERMINATION   OP   NICOTIN   IN   TOBACCO  EXTRACTS. 


Evidently  precipitation  may  be  successfully  carried  out  in  presence 
of  considerable  hydrochloric  acid.  In  such  case  the  liquid  soon  clears, 
but  the  crystals  deposited  are  small  and  it  is  difficult  to  determine 
when  the  change  to  crystalline  form  is  complete.  Tests  2  and  3  made 
altogether  much  the  best  appearance  and  mark  the  limits  of  the 
amount  of  acid  which  should  be  added. 

The  obvious  effect  of  heat  in  lowering  the  percentage  of  nicotin 
recovered  was  at  first  difficult  to  account  for.  Filtrates  from  such 
tests  showed  no  further  precipitation  on  long  standing,  and  subse- 
quent experiments  in  which  the  tests  were  allowed  to  stand  over  night 
before  filtration  showed  similarly  IOAV  results,  namely,  about  0.5  per 
cent  lower  than  those  obtained  by  precipitation  at  room  temperature. 
The  suspicion  arose  that  the  results  obtained  by  precipitating  hot 
were  really  the  correct  ones  and  that  precipitates  formed  and  settled 
at  room  temperature  occluded  silicotungstic  acid.  To  settle  this  ques- 
tion portions  of  a  nicotin  solution  were  precipitated  both  hot  and  cold, 
the  tests  made  cold  of  course  being  allowed  to  stand  over  night  before 
filtration,  while  tests  made  hot  were  filtered  after  cooling  for  about 
one  hour.  The  precipitates  were  filtered  on  paper,  washed  and  dried, 
A  portion  of  each  precipitate  was  then  placed  in  a  weighed  platinum 
crucible,  dried  to  constant  weight  at  120°  to  130°  C.,  and  the  weight 
of  the  dried  precipitate  obtained.  A  weighing  bottle  was  of  course 
employed  to  hold  crucible  and  precipitate  during  weighing.  The 
crucibles  and  precipitates  were  next  ignited,  and  the  weights  of  the 
various  residues  were  obtained.  If  the  precipitate  formed  at  room 
temperature  occludes  silicotungstic  acid  it  should  yield  a  residue 
greater  than  the  theoretical  and  greater  than  the  residue  obtained 
from  the  precipitate  formed  in  hot  solution.  That  such  was  not  the 
case  is  shown  by  the  following  results: 

TABLE  6. — Residues  obtained  by  ignition  of  dried  nicotin  silicotunff state. 


Method  of  precipitation. 

Weight  of 
dried  salt. 

Weight  of 
residue. 

Residue  on 
dried  salt. 

Cold 

Grams. 
1.008 

Gram. 
0.8914 

Per  cent. 
88.43 

Do  

.6902 

.6105 

88.45 

Hot  

.9848 

.8724 

88.59 

Do  

.6914 

.6116 

88.46 

Theoretical  per  cent  of  residue- 88.76. 


The  next  set  of  experiments  involved  the  formation  and  crystalliza- 
tion of  the  precipitate  from  a  mechanically  stirred  liquid  at  room 
temperature,  holding  either  nicotin  or  silicotungstic  acid  in  excess 
throughout,  so  far  as  possible.  Solution  D  of  "  pure  nicotin  "  was 
employed.  Results  appear  in  Table  7. 


THE  SILICOTUNGSTATE   METHOD. 


TABLE  7. — Results  from  precipitation  of  nicotin  silicotungstate  under  various 
of  "pure  nicotin."     Weight  of  sample  taken  for  each  test  =  0.1019  gram. 


No.  of 
test. 

Conditions  of  precipitation. 

Weight  of 
anhydrids. 

Nicotin. 

1 

Volume  of  solution,  100  c.  c.;  added  2c.  c.  dilute  HC1;  left  at  room  tem- 
perature about  20  hours  

Gram. 
0.8662 

Per  cent. 
96  91 

2 

Volume  of  solution  and  acid,  as  in  test  1;  heated  on  steam  bath  J  hour, 
then  left  at  room  temperature  overnight  

8613 

96  37 

3 

Volume  of  solution  and  acid,  as  in  tests  1  and  2;  stirred  mechanically 
overnight  at  room  temperature 

.8657 

96  85 

4 

Volume  of  solution,  50  c.c.;  added  Ic.  c.  dilute  HC1;  Into  this  dropped 
from  burette  solution  of  10  c.  c.  silicotungstic  acid  made  to  50  c.  c.  and 
acidified  with  1  c.  c.  dilute  HC1,  requiring  4  hours  for  complete  addi- 
tion of  the  reagent;  liquid  thoroughly  stirred  during  addition  of  re- 
agent and  overnight;  room  temperature  

.8593 

96.13 

5 

Duplicate  of  test  4.  . 

.8595 

96.16 

6 

Solution  and  reagent  prepared  as  in  tests  4  and  5,  but  precipitated  under 
reverse  conditions,  i.  e.,  by  dropping  the  nicotin  solution  into  the  re- 
agent; stirred  overnight  at  room  temperature  

.8650 

96.77 

The  results  in  Table  7  prove  that  the  composition  of  the  precipitate 
is  variable.  Either  the  precipitate  formed  in  a  cold  solution  in  which 
silicotungstic  acid  is  in  excess  contains  too  much  silicotungstic  acid  or 
the  precipitates  formed  in  cold  solutions  in  presence  of  excess  of  nico- 
tin and  in  all  hot  solutions  contain  too  much  nicotin.  The  results 
shown  in  Table  6  render  the  first  hypothesis  unlikely.  They  do,  how- 
ever, permit  the  second  hypothesis  to  be  entertained,  for  if  too  much 
nicotin  were  in  any  case  contained  in  the  precipitate  it  is  possible  that 
excess  nicotin  might  be  volatilized  during  the  process  of  drying  at 
120°  to  130°  C.  and  hence  leave  the  dried  precipitate  of  normal  com- 
position. Altogether  the  results  given  in  Tables  6  and  7  indicate  that 
quantitative  results  can  be  obtained  only  when  nicotin  is  precipitated 
at  not  over  30°  C.  by  an  immediate  excess  of  silicotungstic  acid.  The 
crystals  of  silicotungstate  thus  obtained  appear  to  possess  a  composi- 
tion which  is  uniform  and  practically  that  demanded  by  theory. 

In  performing  the  experiments  noted  in  Table  7  it  was  observed 
that  freshly  precipitated  nicotin  silicotungstate  very  quickly  became 
crystalline  under  the  action  of  a  mechanical  stirrer.  That  thorough 
and  continued  agitation  is  all  that  is  necessary  to  secure  a  simple  and 
accurate  rapid  modification  of  the  method  is  apparent  from  the  fol- 
lowing results: 

TABLE  8. — Tests  on  rapid  method  based  on  mechanical  stirring,  using  solution  D 
of  "  pure  nicotin."     Weight  of  sample  taken  for  each  test  =  0.1019  gram. 


No.  of 
test. 

Conditions  of  precipitation. 

Weight  of 
anhydrids. 

Nicotin. 

1 

Volume  of  solution,  100  c.  c.;  added  2  c.  c.  dil.  HCI  and  10  c.  c.   silico- 
tungstic acid;  stirred  over  night.    (Taken  from  Table  7,  test  3,  for 

Gram. 
0.8057 

Percent. 

96.85 

2 

As  test  1  except  that  stirred  j  hour  onlv  and  filtered  at  once  

.8645 

96.72 

3 

As  test  2,  except  that  added  5  c.  c.  dil.  HCI  

.8638 

96.64 

In  both  test  2  and  test  3  a  change  in  the  character  of  the  precipitate 
had  become  apparent  in  the  first  10  minutes;  at  the  end  of  the  second 
10  minutes  the  change  to  a  crystalline  form  appeared  to  be  complete. 


20  DETERMINATION    OF   NICOTIN   IN   TOBACCO   EXTRACTS. 

THE    STEAM    DISTILLATION    OF    NICOTIN    PREPARATIONS. 

Since  nicotin  is  evolved  from  boiling  dilute  solutions  with  extreme 
slowness,  in  the  steam  distillation  of  nicotin  preparations  it  is  always 
desirable  to  keep  the  volume  of  liquid  in  the  distillation  flask  at  the 
lowest  practicable  amount.  This  is  essential  in  the  execution  of  the 
Kissling  process,  where  the  distillate  is  later  to  be  titrated,  and  is 
there  easily  accomplished,  since  the  liquid  in  the  flask  contains  but 
a  comparatively  small  amount  of  salts  and  other  extraneous  matter. 
Many  commercial  preparations  contain  a  large  amount  of  such  ex- 
traneous matter,  and  during  direct  distillation  consequently  demand 
that  a  comparatively  large  volume  of  fluid  be  maintained  in  the 
distillation  flask,  with  the  result  that  a  large  volume  of  distillate 
must  be  collected  in  order  to  capture  the  last  traces  of  nicotin.  In 
general,  this  constitutes  no  serious  drawback  to  the  application  of 
the  silicotungstate  method,  for  the  extreme  insolubility  of  nicotin 
silicotungstate  admits  of  its  quantitative  separation  from  very  dilute 
solutions  of  nicotin.  The  greater  length  of  time  required  in  such  a 
direct  steam  distillation  of  a  nicotin  preparation  is  largely  com- 
pensated in  practice  by  the  fact  that  when  once  properly  started 
the  distillation  will  progress  without  the  close  personal  attention  on 
the  part  of  the  analyst  which  is  required  during  the  steam  distillation 
of  the  Kissling  process,  where  the  maintenance  of  the  volume  of 
liquid  at  its  lowest  possible  amount  is  of  great  importance.  In  the 
case  of  high  percentage  nicotin  solutions  it  is  most  convenient  to 
count  on  a  final  volume  of  1,000  c.  c.  for  the  distillate,  in  which  case, 
if  between  1  and  2  grams  of  nicotin  are  present  in  the  whole,  a  50 
or  100  c.  c.  aliquot  will  be  a  proper  and  convenient  amount  to  em- 
ploy for  precipitation.  In  the  case  of  low  percentage  preparations 
the  distillate  may  amount  to  1,500  c.  c.  or  more,  and  it  is  most  con- 
veniently handled  by  transferring  to  a  2,000  c.  c.  graduated  stoppered 
cylinder  and  making  to  the  next  100  c.  c.  mark. 

In  handling  such  low  percentage  preparations  it  is,  of  course,  en- 
tirely possible,  following  the  method  of  Bertrand  and  Javillier,  first 
to  precipitate  the  nicotin  with  silicotungstic  acid,  and  then  to  subject 
the  collected  precipitate,  after  adding  sufficient  alkali,  to  distillation 
with  steam,  thus  securing  a  small  volume  of  liquid  in  the  distillation 
flask  and  a  consequent  small  volume  of  distillate.  A  serious  practi- 
cal objection  to  this  method  is  the  considerable  necessary  consump- 
tion of  the  expensive  silicotungstic  acid.  It  is  possible  that  some 
other  less  costly  material  may  be  appropriate  for  such  a  preliminary 
precipitation,  and  in  fact  some  preliminary  experiments  on  the  use 
of  picric  acid  have  been  tried  in  this  laboratory.  But  if  it  can  possi- 
bly be  avoided  it  seems  very  undesirable  to  introduce  such  a  compli- 
cation into  a  method  which  is  otherwise  consistent  and  uniform.  At 


SUMMARY  AND   CODIFIED  DIRECTIONS.  21 

any  rate,  the  proper  working  out  and  testing  of  such  a  method  would 
require  considerable  time.  For  the  present,  if  it  is  necessary  to 
handle  any  nicotin  preparation  which  absolutely  will  not  permit  dis- 
tillation with  steam  as  the  first  step,  it  is  always  possible  to  extract 
the  material  with  ether  after  the  Kissling  method — restricting  the 
time  of  extraction  to  that  necessary  simply  to  extract  all  nicotin — 
and  to  proceed  with  the  residue  in  the  extraction  flask  according  to 
the  regular  silicotungstate  method. 

SUMMARY  AND   CODIFIED   DIRECTIONS   FOR   ROUTINE   WORK. 

It  appears,  then,  that  the  silicotungstate  method,  a  logical  out- 
growth from  the  work  of  Bertrand  and  Javillier,  is  placed  upon  a 
firm  basis  as  a  scientifically  sound  and  technically  practical  method 
for  the  accurate  and  convenient  determination  of  nicotin  in  nicotin 
solutions  and  tobacco  extracts.  The  results  obtainable  by  the  method 
theoretically  should  be  more  accurate  than  the  results  afforded  by 
the  Kissling  method,  a  hypothesis  supported  by  the  results  of  the 
experimental  work  herein  cited.  Each  step  in  the  process  and  the 
completeness  of  each  operation  may  be  tested  as  the  work  proceeds, 
and  but  little  is  left  dependent  upon  the  judgment  of  the  operator. 
The  method  is  likewise  indicated  to  excel  in  convenience  and  econ- 
omy, for  though  it  employs  an  expensive  reagent  it  demands  but 
comparatively  small  quantities,  and  although  it  is  a  gravimetric 
method,  it  is  simple  and  rapid,  yielding  definite  results  susceptible  of 
close  duplication  with  no  excessive  demands  upon  the  time  or  skill  of 
the  analyst. 

From  the  data  of  experimental  work  the  following  codified  direc- 
tions may  be  offered  for  the  routine  execution  of  analyses  by  the 
silicotungstate  method : 

Weigh  out  such  an  amount  of  the  preparation  as  will  contain  pref- 
erably between  1  and  2  grams  of  nicotin,  except  in  the  case  of  extracts 
high  in  extraneous  matter,  where  not  in  excess  of  30  grams  should 
be  employed ;  wash  with  water  into  a  500  c.  c.  round-bottomed  flask ; 
add  1  to  If  grams  paraffin,  a  few  small  pieces  of  pumice,  and  caustic 
soda  solution  to  strong  alkalinity  (5  to  10  c.  c.  of  NaOH  solution, 
1  to  2).  Distill  in  a  rapid  current  of  steam  through  a  three-bend 
connecting  tube,  a  condenser,  and  adapter  into  10  c.  c.  of  dilute  hydro- 
chloric acid  (1  to  4)  in  a  capacious  flask.  When  distillation  is  well 
started,  apply  heat  to  the  distillation  flask  (a  Babo  funnel  is  most 
convenient)  to  reduce  the  volume  of  liquid  as  far  as  practicable  with- 
out bumping  or  undue  separation  of  insoluble  matter.  Continue  dis- 
tillation until  a  few  cubic  centimeters  of  the  distillate  collected  from 
the  condenser  after  removal  of  the  adapter  show  no  cloud  or  opales- 
cence  when  treated  with  a  drop  of  silicotungstic  acid  solution  followed 
by  a  drop  of  dilute  hydrochloric  acid  (1  to  4).  Prove  alkalinity  of 


22  DETERMINATION    OF   NICOTIN    IN    TOBACCO   EXTRACTS. 

the  residue  in  the  distillation  flask  with  phenolphthalein  solution  or 
paper. 

Make  the  distillate  to  convenient  volume,  mix  well  and  pass  through 
a  large  dry  filter,  discarding  a  liberal  first  portion  of  the  filtrate,  and 
test  a  portion  with  methyl  orange  to  assure  its  acidity.  Pipette  into 
a  beaker  an  aliquot  containing  about  0.1  gram  nicotin,  add  for  each 
100  c.  c.  of  liquid  3  c.  c.  of  dilute  hydrochloric  acid  (1  to  4) — or  more, 
if  indicated  necessary  by  the  test  with  methyl  orange — and  add  1  c.  c. 
of  a  12  per  cent  solution  of  silicotungstic  acid  for  each  0.01  gram 
nicotin  supposed  to  be  present.1  Stir  thoroughly  and  let  stand  for 
eighteen  hours.2  Then  sfir  up  the  precipitate,  making  sure  that  it 
settles  quickly  and  completely  in  crystalline  form ;  filter  on  a  quanti- 
tative paper,  and  wash  with  cold  water  containing  1  c.  c.  of  concen- 
trated hydrochloric  acid  per  liter.  Test  the  first  portion  of  the  filtrate 
with  a  few  drops  of  nicotin  distillate  to  prove  excess  of  silicotungstic 
acid. 

Continue  washing  for  two  or  three  fillings  of  the  filter  after  no 
more  opalescence  appears  when  a  few  cubic  centimeters  of  fresh 
filtrate  is  tested  with  a  few  drops  of  nicotin  distillate.  Bring  the 
wet  paper  and  precipitate  into  a  weighed  platinum  crucible,  using 
a  scrap  of  moistened  filter  paper  to  transfer  any  precipitate  which 
may  have  crept  up  the  sides  of  the  funnel ;  dry  carefully,  carbonize, 
and  finally  burn  off  the  carbon  at  as  low  a  temperature  as  possible. 
Gradually  increase  the  heat  and  occasionally  rotate  the  crucible  to 
expose  all  parts  of  the  residue.  At  last  ignite  the  inclined  crucible 
thoroughly  over  the  full  heat  of  a  Bunsen  burner,  finishing  with  five 
to  ten  minutes — not  longer — over  a  powerful  Teclu  burner,  or  five 
minutes  over  a  moderately  powerful  blast  lamp.  Cool  in  a  desiccator. 
The  weight  of  the  residue  multiplied  by  0.114 3  affords  the  weight 
of  nicotin  in  the  aliquot  taken  for  precipitation.  If  the  highest  possi- 
ble degree  of  accuracy  is  desired,  filter  the  precipitate  on  a  weighed 
Gooch  crucible,  dry  at  125°  C.,  and  weigh  the  anhydrous  nicotin  sili- 
cotungstate  as  indicated  on  page  13. 

1  An  excess  of  17  to  18  per  cent  over  the  amount  theoretically  necessary  Is  here  pro- 
vided, allowing  for  all  ordinary  variations. 

1  This  length  of  time  is  probably  more  than  Is  necessary,  but  in  the  absence  of  positive 
evidence  it  is  wiser  to  prescribe  it.  For  quick  results  use  a  mechanical  stlrrer,  as  Indi- 
cated on  page  10. 

8  The  factor  given  by  Bertrand  and  Javilller  Is  0.1139  and  Is  apparently  based  upon  an 
erroneous  calculation,  since  other  calculations  cited  by  them  check  with  those  performed 
In  this  laboratory  upon  the  basis  of  the  most  recent  available  atomic  weights.  The  factor 
is  actually  slightly  over  0.1140. 

o 


from  which  it  was  borrowed. 


1 A  1995 
/Jill  0  7  J995 


SRL 

QUARTER 


Univers 

SoutJ 

Libr 


